Preparation Preheat oven to 350°F with rack in middle. Whisk together flour, cornmeal, cornstarch, and salt. Blend butter, confectioners sugar, vanilla, and zest in a food processor until creamy, about 30 seconds. Scrape down side of bowl, then add all of flour mixture and pulse until dough just begins to come together. Roll out dough on a well-floured surface with a well-floured rolling pin to 1/3 inch thick. Cut out as many rounds as possible with a 2-inch round cookie cutter or drinking glass and transfer to an ungreased large baking sheet. Reroll scraps and cut out more rounds. Sprinkle tops with granulated sugar. Bake until undersides are pale golden, 12 to 14 minutes. Transfer to a rack to cool.
Preparation Preheat oven to 350°F with rack in middle. Whisk together flour, cornmeal, cornstarch, and salt. Blend butter, confectioners sugar, vanilla, and zest in a food processor until creamy, about 30 seconds. Scrape down side of bowl, then add all of flour mixture and pulse until dough just begins to come together. Roll out dough on a well-floured surface with a well-floured rolling pin to 1/3 inch thick. Cut out as many rounds as possible with a 2-inch round cookie cutter or drinking glass and transfer to an ungreased large baking sheet. Reroll scraps and cut out more rounds. Sprinkle tops with granulated sugar. Bake until undersides are pale golden, 12 to 14 minutes. Transfer to a rack to cool.